I upgraded today from a DX10.1 ATI 4890 1GB to a DX11 6950 2GB, almost got the Nvidia 570 GTX but I wasnt convinced it was worth the extra £30 given the 6950 has more vram and I can overclock it to near 580 performance.
IMHO Nvidia have a great GPU in the pipe in the form of 'Kepler', promised to double++ the performance that of 'Fermi'! The only downside is that it's due out Q1/Q2 next year but it could be a card to wipe the floor
if priced correctly.
I think thats bad timing for Nvidia because mass market PC gamers are eying up Battlefield3 due out Q4 2011, that is the killer app for the GPU market atm.
You can't beat the performance value of the ATI 6950 atm, but I do think the next round will favour Nvidia in 9 months time. The main question though is will we have the games that use that much GPU power short of users with 3+ screens?